In modern society, the ready availability and access to mobile radio communication systems through which to communicate is a practical necessity. Cellular, and cellular-like, communication systems are exemplary radio communication systems whose infrastructures have been widely deployed and regularly utilized by many. Successive generations of cellular communication systems have been developed, and their operating parameters and protocols are set forth in standards promulgated by standard-setting bodies. And, successive generations of network apparatus have been deployed, each operable in conformity with an associated operating standard.
Early-generation cellular communication systems provided voice communication services and limited data communication services. Successor-generation, cellular communication systems provide increasingly data-intensive communication services. Differing operating standards not only provide different communication capabilities, but utilize different communication technologies and differing frequencies of operation in different frequency bands. The installation of different types of cellular communication systems is sometimes geographically dependent. That is to say, in different areas, network infrastructures, operable pursuant to different types of operating standards, are deployed. The network infrastructures deployed in the different areas are not necessarily compatible. A mobile station operable to communicate by way of network infrastructure constructed in conformity with one operating specification is not necessarily operable to communicate by way of network infrastructure operable pursuant to another operating standard.
So-called, multi-mode mobile stations have been developed that provide the mobile station with communication capability in more than one, i.e., multiple, communication systems, which also operate at different frequencies in different frequency bands. Generally, such multi-mode mobile stations automatically select the manner by which the mobile station is to be operable, responsive to the detected network infrastructure in whose coverage area that the mobile station is positioned. If positioned in the coverage area of the network infrastructures of more than one type of communication system with which the mobile station is capable of communicating, selection of a network infrastructure through which to communicate is made pursuant to a preference scheme, or manually. When provided with multi-mode capability, the mobile station contains circuitry and circuit elements permitting its operation to communicate pursuant to each of the communication systems. Most simply, a multi-mode mobile station is formed of separate circuitry, separately operable to communicate pursuant to the different operating standards. Sometimes, to the extent that circuit elements of the different circuit paths can be shared, parts of the separate circuit paths are constructed to be intertwined, or otherwise shared. By sharing circuit elements, the circuitry size and part count is reduced, resulting in cost and size savings.
Sharing of antenna transducer elements between the different circuit paths, however, presents unique challenges. The required size of an antenna transducer element is, in part, dependent upon the frequencies of the signal energy that is to be transduced by the transducer element. And, as mobile station constructions become increasingly miniaturized, housed in housings of increasingly small package sizes, antenna transducer design becomes increasingly difficult, particularly in multi-mode mobile stations when the different modes operate at different frequencies. Significant effort has been exerted to construct an antenna transducer, operable over multiple frequency bands, and also of small dimension to permit its positioning within the housing of a mobile station of compact size.
A PIFA (Planar Inverted-F Antenna) has been used in multi-mode mobile stations because of its relatively compact size, low profile and because it permits dual-band radiation, however, PIFA antennas have narrow bandwidths. In order to enhance the bandwidth of a PIFA, the structure of the PIFA is sometimes combined together with a parasitic element, or a multi-layered, three-dimensional structure. Such additions, however, increase the volumetric dimensions of the antenna, as well as its weight. The additional resonant branches make the antenna difficult to tune and sometimes introduce EMC and EMI, which interferes with transducing of signal energy. A need therefore exists for an improved small-dimension antenna structure which is also capable of use in multiple different frequency bands.
It is in light of this background information related to antenna transducers for radio devices that the significant improvements of the present invention have evolved.